Women's representation in Parliament: the U.S. still lagging behind

Last weekend was International Women's Day, which promoted various medias and institutions to take a closer look at women's political representation around the world.
As it turns out, 2008 was a milestone for women's representation in Parliaments worldwide: nearly 18 percent of the world's parliamentarians are women - a rise of 4.7 percent compared to 1995, according to the Inter-Parliamentary Union (IPU) (IPU has been following parliamentary turnovers in 51 countries, 61 chambers of parliament, over the last 12 years).
Additionally in 2008, a diverse range of countries (Belarus, New Zealand, Spain, Macedonia…) have reached the United Nations minimum target of 30 percent of women in parliament. The IPU report also highlights an incredible success story. In 2008, Rwanda became the very first country in the world to have women representing more than 50% of the Parliament (56.3%)- a success that can be attributed to strong political will and both legislated and voluntary quotas to guarantee women's place in Parliament (another explanation could be the human cost of the war that has killed many Rwandan men). Other success stories in Africa include Angola where, in its first election since 1992, 37.3% of women now hold seats in Parliament. As for the United States, both houses of Congress elected their highest number of women members (17% in each chamber), but the country actually ranks below the global average. Actually, in the World Economic Forum 2008 "Global Gender Gap Report", the USA ranks 64th in the Women in Parliament Index (it ranks 56th in the more general "Women Political Empowerment index, and 27th in the global Gender Gap ranking, that takes into account sociological and economical data such as economic participation wage equality, education attainment…)
These global progresses might sound encouraging, even though the pace of reform is very slow: it is estimated that it would be another 70 years before women achieved full parity with men in politics. A quarter of chambers are comprised of less than ten percent female members, and some regions (such as the Pacific Islands) show no progress at all.
Voting systems are one important, often overlooked variable that can explain these wide discrepancies in women's representation. The IPU report states, "in the 14 single/lower houses using proportional representation, women won an average of 24.5% of seats". Additionally, "in the 10 chambers using mixed electoral systems, women were elected to 21.4% of the seats"… in sharp contrast with the poor 18% of women elected in the 22 chambers using majority electoral systems.
PR electoral systems provide greater opportunities for increasing women's representation, such as by introducing special measures or quotas and allowing voters to elect members of choice. Generally speaking, "as candidates are elected on political party lists", the report explains, "Political parties are afforded the opportunity to nominate women in winnable positions". Parties can promote women's candidacies through their own channels, so women are not competing directly with men in a single member constituency. With PR, women can be more easily promoted if the parties so desire and there is that political will.